This invention relates to evaporative emission control systems of the type that are commonly used in association with internal combustion engines of automotive vehicles.
In such an evaporative emission control system, excess fuel vapors from the fuel tank are collected in a canister which must be periodically purged to the engine's induction system so that the vapors can pass into the engine's cylinders for combustion. In this way, the excess vapors do not escape to atmosphere where they may otherwise contribute to air pollution. The periodic purging of the vapor collection canister is conducted when conditions conducive to purging exist, and therefore it is a customary practice to have a canister purge solenoid (CPS) valve exercise control over the venting of the canister to the induction system and to place the CPS under the control of the engine electronic control unit (ECU). Because the ECU receives signals representing various engine operating parameters, it can be programmed to allow purging of the canister at different rates depending upon the prevailing engine operating conditions. Thus at certain times, greater amounts of purging may be permitted while at others, lesser amounts may be allowed.
Governmental regulations establish limits for the amount of fuel vapor that is permitted to be emitted from an automotive vehicle to atmosphere. The establishment of stricter regulations may impose heavier burdens on evaporative emission control systems such that the present systems may not be able to achieve compliance. Accordingly, there is a need for further improvement in the existing evaporative emission control systems of automotive vehicles so that increased flow rates of excess fuel vapors can be successfully handled without sacrificing low flow rate accuracy. The present invention is directed to a solution for meeting this need.
Drawing FIGS. 1-4 relate to an embodiment which comprises the inclusion of a variable orifice in the vapor flow path from the canister to the induction system and the use of the engine's throttle to exercise control over the degree of restriction imposed by the variable orifice on the vapor flow path to the induction system. The invention of these four drawing figures is the subject of commonly assigned U.S. Pat. No. 4,995,369 of which Ser. No. 07/490,791, filed Mar. 8, 1990, is a continuation-in-part. The variable orifice is progressively increasingly restricted as the engine is progressively increasingly throttled. A purge regulator that is under the control of the engine ECU also exercises control over the vapor flow to the induction system. The ECU is programmed using conventional programming techniques to produce a desired degree of purge flow regulation in accordance with engine operating conditions detected by the ECU. Thus, certain principles of the invention of Ser. No. 07/490,791 contemplate the conjoint control of the vapor flow from the canister to the induction system by the throttle's control of the variable orifice and by the ECU's control of the purge regulator.
A modern internal combustion engine that contains an ECU typically has a throttle position sensor that provides to the ECU an indication of the instantaneous throttle position. By having the variable orifice directly controlled by the throttle, the throttle position sensor signal is made inherently representative of the degree of restriction imposed by the variable orifice on vapor flow from the canister to the induction passage. Thus, the ECU can "read" the variable orifice and take that reading into account as it exercises control over the purge regulator. A system embodying such inventive principles is well suited for providing controlled canister purging over a large dynamic range extending from engine idle to wide open throttle. It is also capable of providing a steadier flow that is beneficial in attenuating hydrocarbon emission spikes in the engine exhaust.
FIGS. 5 through 9 of the drawings relate to a novel construction for coupling the purge valve with the movable wall (diaphragm) that operates it. A rod that is guided for linear motion has one end connected to the movable wall and the other end to the purge valve. The connection to the movable wall is through a joint that essentially precludes the transmission of any bending moment from the movable wall to the rod. The connection to the valve provides for a certain wobble of the valve head that is advantageous for proper seating on the valve seat while preventing fluid leakage through the connection. The combination of these features enhances the accuracy of response of the device to commands.
FIG. 10 relates to an embodiment of purge regulator in which the construction of the vacuum regulator is different from that of the vacuum regulator of FIG. 5.
FIGS. 11-16 relate to additional embodiments which are in certain respects improvements upon the embodiments of FIGS. 5-10. A common feature of the additional new embodiments relates to a tapered valve element for controlling the purge flow. As the valve begins to increasingly open from its fully closed condition, the tapered portion of the valve element coacts with a portion of the flow passage circumscribed by the valve seat to create a gradual increase in the controlled restriction that is imposed by the valve, as distinguished from a more abrupt increase that would occur in a construction like that of FIG. 5. The advantages of this result of incorporating a tapered valve element into the purge regulator include: reduction in the purge flow oscillations which might otherwise occur in a construction that has a more abrupt opening characteristic; operating noise reduction due to the attenuation of the purge flow oscillations; a reduction in the number of components that are required, thereby enabling meaningful reductions in overall valve size to be made, and simplifying fabrication procedures; the ability to attain a more linear characteristic for flow output vs. signal input; and as a result of the more linear flow characteristic, better compatability for open loop operation at low duty cycles (idle purge), yet retaining high duty cycle compatability for closed-loop operation.
The foregoing features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims, which should be considered in conjunction with the accompanying drawings. The drawings disclose a presently preferred embodiment of the invention in accordance with the best mode contemplated at this time in carrying out the invention.